In the semiconductor industry, various manufacturing processes are typically carried out on a substrate (e.g., a semiconductor wafer) in order to achieve various results on the substrate. Processes such as ion implantation, for example, can be performed in order to obtain a particular characteristic on or within the substrate, such as limiting a diffusivity of a dielectric layer on the substrate by implanting a specific type of ion. In the past, ion implantation processes were performed in a batch process, wherein multiple substrates were processed simultaneously by being placed on a disk and rotated at high speed past a stationary ion beam to constitute one dimension of the scan, while the rotating disk itself was translated to provide a second scanning axis. Later implantation system employed a serial process, wherein a single substrate is individually processed.
In a typical serial process an ion beam is either scanned in a single axis across a stationary wafer, wherein the wafer is translated in one direction past a fan-shaped, or scanned ion beam, or the wafer is translated in generally orthogonal axes with respect to a stationary ion beam or “spot beam”.
Translating the wafer in generally orthogonal axes requires a uniform translation and/or rotation of the wafer in order to provide a uniform ion implantation across the wafer. Furthermore, such a translation should occur in an expedient manner, in order to provide acceptable wafer throughput in the ion implantation process. Due to the slower reciprocating motion of the workpiece, the two dimensional scanning system is not capable of the same scanning speeds as the batch tools. Further, because of this slower scan speed the number of scan lines across the wafer is reduced, and therefore the micro-uniformity of the dose across the wafer is an issue to be considered.
One prior art attempt to address the micro-uniformity issue was to select the pitch of the scan lines based on a beam measurement and prediction of the resultant uniformity. Although this solution can be effective for controlling uniformity, it has a disadvantage that the decreasing the pitch of the scan lines increases the total implant time because of the corresponding greater number scan passes required to completely scan the workpiece. Thus the prior art solution provides for sufficient uniformity, but such improvement comes at the expense of a decrease in the productivity of the tool.
Accordingly, there is a need for improvement in two dimensional scanning systems.